The deployment of the road-mobile missile system has been planned at least since July, but its arrival in Crimea coincides with a flurry of military activity and rhetoric following claims from the Kremlin that two Russians were killed on the Crimean-Ukrainian border last week

Russia has deployed an advanced S-400 surface-to-air missile battery to the Crimean Peninsula amid escalating tensions there, according to Russian news reports. The missile system, once operational, would be able to target aircraft deep into Ukrainian airspace.

The deployment of the road-mobile missile system has been planned at least since July, but its arrival in Crimea coincides with a flurry of military activity and rhetoric following claims from the Kremlin that two Russians were killed on the Crimean-Ukrainian border last week.

The S-400 can hit targets well over 150 miles from its launch site when paired with the appropriate radar array and is billed as one of Russia’s most advanced surface-to-air defense systems. The Crimean Peninsula is currently home to the older S-300 Russian surface-to-air missiles that will probably be replaced by the arrival of the newer S-400s.

Between Aug. 6 and Aug. 8, the Russian Federal Security Service, or FSB, said it arrested Ukrainian saboteurs who had sneaked over the border and also recovereda large cache of explosives in the town of Armyansk. During the arrest, one FSB agent was killed in an exchange of gunfire with the Ukrainian agents, according to a statement on the FSB’s website. The FSB also claimed to have repelled Ukrainian special forces attempting to infiltrate Crimea and in a subsequent cross-border shelling, one Russian soldier was apparently killed.

Eyewitness accounts to the incident have been spotty, and social media reports indicate there were Internet outages in northern Crimea during the FSB operation. The Ukrainian government has denied that it condoned any type of border incursion or that it had shelled Russian forces from its territory.